Fourier Transform spectra of heated $(230^{\circ}$ C) $12_{C_{2}H4}$ and ${^{12}}C^{13}CH_{4}$ ethylenes have been recorded from 840 to $1040 cm^{-1}$ using the F.T. Spectrometer of the Laboratoire de Spectronomie Moleculaire with an apparatus function of $4\times 10^{-3}cm^{-1}$ (F.W.H.M.) and an absolute absolute precision of $2\times 10^{-4} cm^{1}$. The quality of the spectra yields to the first observation of the three most intense hot bands of both isotopes. These hot bands, $\nu_{7}+\nu_{10}-\nu_{10}, \nu_{7}+\nu_{8}-\nu_{8}$ and $2\nu_{7}-\nu_{7}$, are involved in the optical pumping processes of ethylene with $CO_{2}$ and $N_{2}O$ lasers. Furthermore, for ${^{12}}C_{2}H_{4}$, the analysis of the $\nu_{7}+\nu_{8}$ band on the basis of F.I. spectra combinated with the observation of the $\nu_{7}+\nu_{8}-\nu_{8}$ band leads to the full determination and the analysis of the isolated Raman active $\nu_{8}$ level with and accuracy better than $0.001 cm^{-1}$. The study of $\nu_{7}+\nu_{1}0$ and $2\nu_{7}$ is much more complicated because they are strongly coupled with at least five other levels. The analysis model will be discussed. Ch. LAMBEAU M. DE VLEESCHOUWER, A. FAYT AND G. GUELACHVILI to be published.